1. Field of the Invention
The present invention relates in general to automotive automatic transmissions, and more particularly to a device for reducing a select shock of the automatic transmissions.
2. Description of the Prior Art
In order to clarify the task of the present invention, one conventional select shock reducing device for the automatic transmission will be described, which is disclosed in Japanese Patent First Provisional Publication 1-105050.
The select shock reducing device of this publication comprises generally an accumulator which controls ON/OFF operation of friction elements which are essential to all forward speeds and a reverse, a sensor means which detects starting of engaging movement of the friction elements, and a control means which raises the back pressure of the accumulator for a period from the time when a new range is selected by the transmission select lever to the time when the sensor means detects the starting of engaging movement of the friction elements. That is, when the transmission select lever is moved from neutral to a range which will produce a forward speed, the control means increases the back pressure of the accumulator to raise hydraulic pressure applied to the friction elements. With this, the starting of the engaging movement of the friction elements is quickly carried out. When thereafter the sensor means detects the starting of engaging movement of the friction elements, the control means reduces the back pressure of the accumulator to a normal level. With this, the accumulator can gently increase the hydraulic pressure applied to the friction elements.
However, this conventional select shock reducing device has no measure against a trouble of the sensor means. That is, when the sensor means gets out of order, the starting of engaging movement of the friction elements can not be detected, and thus, the hydraulic pressure applied to the friction elements can not be reduced to the normal level even when the engaging movement of the friction elements starts. Thus, under such condition, the select shock is deteriorated.
The sensor means employed in the select shock reducing device of the publication is constructed to find the starting of the engaging movement of the friction elements by detecting a reduction in rotation speed of the turbine of the associated torque converter. Thus, when the movement of the transmission select lever does not induce a marked speed reduction of the turbine like in the selection during cruising of the vehicle, it is impossible to sense the starting of the engaging movement of the friction elements.